#include "iwsha2.h"
#include <string.h>
#include <stdio.h>

#define CHUNK_SIZE 64
#define TOTAL_LEN_LEN 8

/*
 * Comments from pseudo-code at https://en.wikipedia.org/wiki/SHA-2 are reproduced here.
 * When useful for clarification, portions of the pseudo-code are reproduced here too.
 */

/*
 * Initialize array of round constants:
 * (first 32 bits of the fractional parts of the cube roots of the first 64 primes 2..311):
 */
static const uint32_t k[] = {
  0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
  0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
  0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
  0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
  0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
  0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
  0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
  0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

struct buffer_state {
  const uint8_t *p;
  size_t len;
  size_t total_len;
  int single_one_delivered; /* bool */
  int total_len_delivered; /* bool */
};

IW_INLINE uint32_t right_rot(uint32_t value, unsigned int count) {
  /*
   * Defined behaviour in standard C for all count where 0 < count < 32,
   * which is what we need here.
   */
  return value >> count | value << (32 - count);
}

static void init_buf_state(struct buffer_state *state, const void *input, size_t len) {
  state->p = input;
  state->len = len;
  state->total_len = len;
  state->single_one_delivered = 0;
  state->total_len_delivered = 0;
}

/* Return value: bool */
static int calc_chunk(uint8_t chunk[CHUNK_SIZE], struct buffer_state *state) {
  size_t space_in_chunk;

  if (state->total_len_delivered) {
    return 0;
  }

  if (state->len >= CHUNK_SIZE) {
    memcpy(chunk, state->p, CHUNK_SIZE);
    state->p += CHUNK_SIZE;
    state->len -= CHUNK_SIZE;
    return 1;
  }

  memcpy(chunk, state->p, state->len);
  chunk += state->len;
  space_in_chunk = CHUNK_SIZE - state->len;
  state->p += state->len;
  state->len = 0;

  /* If we are here, space_in_chunk is one at minimum. */
  if (!state->single_one_delivered) {
    *chunk++ = 0x80;
    space_in_chunk -= 1;
    state->single_one_delivered = 1;
  }

  /*
   * Now:
   * - either there is enough space left for the total length, and we can conclude,
   * - or there is too little space left, and we have to pad the rest of this chunk with zeroes.
   * In the latter case, we will conclude at the next invokation of this function.
   */
  if (space_in_chunk >= TOTAL_LEN_LEN) {
    const size_t left = space_in_chunk - TOTAL_LEN_LEN;
    size_t len = state->total_len;
    int i;
    memset(chunk, 0x00, left);
    chunk += left;

    /* Storing of len * 8 as a big endian 64-bit without overflow. */
    chunk[7] = (uint8_t)(len << 3);
    len >>= 5;
    for (i = 6; i >= 0; i--) {
      chunk[i] = (uint8_t) len;
      len >>= 8;
    }
    state->total_len_delivered = 1;
  } else {
    memset(chunk, 0x00, space_in_chunk);
  }

  return 1;
}

/*
 * Limitations:
 * - Since input is a pointer in RAM, the data to hash should be in RAM, which could be a problem
 *   for large data sizes.
 * - SHA algorithms theoretically operate on bit strings. However, this implementation has no support
 *   for bit string lengths that are not multiples of eight, and it really operates on arrays of bytes.
 *   In particular, the len parameter is a number of bytes.
 */
void iwsha256(const void *input, size_t len, uint8_t hash_out[32]) {
  /*
   * Note 1: All integers (expect indexes) are 32-bit unsigned integers and addition is calculated modulo 2^32.
   * Note 2: For each round, there is one round constant k[i] and one entry in the message schedule array w[i], 0 = i = 63
   * Note 3: The compression function uses 8 working variables, a through h
   * Note 4: Big-endian convention is used when expressing the constants in this pseudocode,
   *     and when parsing message block data from bytes to words, for example,
   *     the first word of the input message "abc" after padding is 0x61626380
   */

  /*
   * Initialize hash values:
   * (first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19):
   */
  uint32_t h[] = { 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };
  unsigned i, j;

  /* 512-bit chunks is what we will operate on. */
  uint8_t chunk[64];

  struct buffer_state state;

  init_buf_state(&state, input, len);

  while (calc_chunk(chunk, &state)) {
    uint32_t ah[8];

    const uint8_t *p = chunk;

    /* Initialize working variables to current hash value: */
    for (i = 0; i < 8; i++) {
      ah[i] = h[i];
    }

    /* Compression function main loop: */
    for (i = 0; i < 4; i++) {
      /*
       * The w-array is really w[64], but since we only need
       * 16 of them at a time, we save stack by calculating
       * 16 at a time.
       *
       * This optimization was not there initially and the
       * rest of the comments about w[64] are kept in their
       * initial state.
       */

      /*
       * create a 64-entry message schedule array w[0..63] of 32-bit words
       * (The initial values in w[0..63] don't matter, so many implementations zero them here)
       * copy chunk into first 16 words w[0..15] of the message schedule array
       */
      uint32_t w[16];

      for (j = 0; j < 16; j++) {
        if (i == 0) {
          w[j] = (uint32_t) p[0] << 24 | (uint32_t) p[1] << 16 |
                 (uint32_t) p[2] << 8 | (uint32_t) p[3];
          p += 4;
        } else {
          /* Extend the first 16 words into the remaining 48 words w[16..63] of the message schedule array: */
          const uint32_t s0 = right_rot(w[(j + 1) & 0xf], 7) ^ right_rot(w[(j + 1) & 0xf], 18) ^ (w[(j + 1) & 0xf] >> 3);
          const uint32_t s1 = right_rot(w[(j + 14) & 0xf], 17) ^ right_rot(w[(j + 14) & 0xf], 19) ^ (w[(j + 14) & 0xf] >> 10);
          w[j] = w[j] + s0 + w[(j + 9) & 0xf] + s1;
        }
        const uint32_t s1 = right_rot(ah[4], 6) ^ right_rot(ah[4], 11) ^ right_rot(ah[4], 25);
        const uint32_t ch = (ah[4] & ah[5]) ^ (~ah[4] & ah[6]);
        const uint32_t temp1 = ah[7] + s1 + ch + k[i << 4 | j] + w[j];
        const uint32_t s0 = right_rot(ah[0], 2) ^ right_rot(ah[0], 13) ^ right_rot(ah[0], 22);
        const uint32_t maj = (ah[0] & ah[1]) ^ (ah[0] & ah[2]) ^ (ah[1] & ah[2]);
        const uint32_t temp2 = s0 + maj;

        ah[7] = ah[6];
        ah[6] = ah[5];
        ah[5] = ah[4];
        ah[4] = ah[3] + temp1;
        ah[3] = ah[2];
        ah[2] = ah[1];
        ah[1] = ah[0];
        ah[0] = temp1 + temp2;
      }
    }

    /* Add the compressed chunk to the current hash value: */
    for (i = 0; i < 8; i++) {
      h[i] += ah[i];
    }
  }

  /* Produce the final hash value (big-endian): */
  for (i = 0, j = 0; i < 8; i++) {
    hash_out[j++] = (uint8_t)(h[i] >> 24);
    hash_out[j++] = (uint8_t)(h[i] >> 16);
    hash_out[j++] = (uint8_t)(h[i] >> 8);
    hash_out[j++] = (uint8_t) h[i];
  }
}

void iwsha256str(const void *input, size_t len, char str_out[65]) {
  uint8_t hash[32];
  iwsha256(input, len, hash);
  iwhash2str(hash, str_out);
}

void iwhash2str(uint8_t hash[32], char str_out[65]) {
  for (int i = 0; i < 32; i++) {
    str_out += sprintf(str_out, "%02x", hash[i]);
  }
}
